The invention concerns a multiflow turbojet-engine thrust-reverser cold-flow duct equipped with a system of combined air takeoffs.
The search for high performance in modern turbojet engines has led to high operational temperatures which, in turn, require air cooling of various engine parts undergoing strong stresses or located in especially hot zones. As regards the turbojet engines of which the applications require a thrust reverser which may, in particular, be associated with the cold flow of fan engines, it is conventional to tap or withdraw air from the cold-flow duct of the thrust reverser. Illustratively the French patent No. A 2 490 731 describes the overall structure of a thrust reverser mounted on the cold-flow duct of a multiflow turbojet engine.
These air takeoffs as a rule are distributed longitudinally (as seen along a generatrix of the cold-flow duct) along the duct wall, depending on the use of the tapped air. Accordingly, the duct wall comprises orifices which are distributed peripherally and which ensure the ventilation of the hot compartment between the wall of the cold-flow duct and the casing of the inside engine, where this wall constitutes the housing of the turbojet engine gas generator. In this manner, the inner surface of said wall is cooled as well as the outer surface of said housing and the various accessories typically mounted on it. The duct may be provided with air intakes of diverse types, such as those which are flush or are dynamic scoops and from which a conduit guides the tapped air to one of the selected points to be cooled. For instance, the air maybe directed to where the engine turbine is located; to ventilate the engine pod; or ventilate the aircraft in general after having crossed a heat exchanger wherein circulates the high-pressure air tapped for the needs of the aircraft. These takeoffs may be located in any of the walls of the reversing duct: inner wall; outer wall; upper or lower divider. In these known devices, the air is tapped individually.
FIG. 1 schematically shows such a design wherein 1 is the radially inner wall of a thrust-reverser cold-flow duct. Holes 2 are present in this wall and downstream, and longitudinally apart, there are flush air intakes 3 extending into a conduit 4 guiding the tapped air toward zones in the aircraft or onto engine parts which are to be cooled, ventilated, or pressurized. The arrow F1 denotes the flow in the duct, the arrow F2 the main takeoff implemented through the air intakes 3 and the arrow F3 the secondary takeoff through the holes 2. The secondary air takeoff F3 through the holes 2 is used in particular to ventilate the housing in which the gas generator or primary part of the turbojet engine is located.
These known designs suffer from drawbacks due to the persistency of viscous boundary layers in the tapped air flows, whereby much of the effectiveness is lost in cooling or ventilating. FIG. 1a schematically shows an air intake 3 wherein a slope, desired to be larger than 15.degree. to improve tapping efficiency, generates turbulent boundary layers. It will be noted that the effective cross-section S'.sub.1 is reduced in relation to the theoretical takeoff cross-section S. Indeed, the average pressure over the height of the tapped fluid flow also is lowered by the boundary layers of which the flow rates and total pressures are decreased. The overall performance of the unit therefore is decreased. The object of the invention is to avert these drawbacks.